*5.1. Multilayer and Nanomultilayer Coatings*

Multilayered coatings comprise at least two different layers, and most commonly this is a periodic repetition of two or more layers. The most frequently used is the classic ... A/B/A/B/A ... type of layering, where the same two layers are sequentially repeated. When the periodicity is within the size scale of up to a few tenths of nanometers, the terms nanomultilayers or nanolayered coatings are often used. The sublayers can be synthesised using different strategies. Keeping the same (nominal) coating chemistry, a variation of the process parameters, such as bias or deposition pressure, can be used to create layers of different stress states, for example. Changing the reactive gas composition is a further approach to alternate nitride, oxynitride and oxide layers on the same metal base, for example. Perhaps most common though is the combination of heterogeneous coating materials obtained through the inclusion of targets of different composition in the PVD deposition system. Furthermore, particularly in industrial-scale deposition systems, codeposition from spatially separated deposition sources with different target materials may be combined with substrate rotation to create multilayered coatings. There are a variety of different approaches for the materials used in the second single layers. Some examples are shown below.
